1. Field of the Invention
The present invention relates to an image transfer fixation apparatus that adopts at least a certain image transfer system/scheme among a variety of image transfer systems/schemes, and an image formation apparatus that is provided with such an image transfer fixation apparatus. A few examples of such an image transfer fixation apparatus and an image formation apparatus include but not limited to a copier, a printer, a facsimile, and a multi-function apparatus that has a combined function of any or all of those enumerated above.
2. Description of the Related Art
In the technical field to which the present invention pertains, an image formation apparatus is widely known. An example of an image formation apparatus known in the art performs image transfer and image fixation as follows. An image is formed on a photosensitive member, which functions as an image carrier. The image that is formed on the photosensitive member is transferred to an intermediary image transfer member by means of a primary image transfer unit. The image that is transferred onto the intermediary image transfer member is further transferred to a certain image transfer target matter/object with the use of a secondary image transfer unit. Thereafter, the image is fixed thereon by means of a certain image fixation unit. A conventional image formation apparatus typically performs image transfer and image fixation as two individual steps, which are executed separately from each other. Recently, however, an image formation apparatus that is provided with a so-called image transfer fixation apparatus and performs image transfer and image fixation at the same time and/or as a single step has been proposed. There are some types of image transfer fixation that have been proposed by the related art so far. An image formation apparatus that is provided with an image transfer fixation apparatus of related art performs secondary image transfer fixation by transferring an image from an intermediary image transfer member onto an image transfer target matter and fixing the image thereon. Another image formation apparatus that is provided with another image transfer fixation apparatus of related art performs secondary image transfer by transferring an image from an intermediary image transfer member onto an image transfer fixation member and thereafter performs tertiary image transfer as well as image fixation by transferring the image from the image transfer fixation member onto an image transfer target matter and fixing the image thereon. In both types of the related-art image transfer fixation described above, fine particles that have electrification characteristics and are mainly made of a resin called as toner are typically used.
In the operation flow of an electro-photographic image formation apparatus, it is the step of transferring an image onto an image transfer target matter that has considerable influence upon the quality of an image formed thereon. Paper is usually used as an image transfer target matter. There are various thickness types thereof including standard paper and thick paper, without any limitation thereto. In addition, there are various surface types thereof. Some of them are smooth, while others are rough. Especially when a sheet of printing paper that has a rough surface is used, the surface of an intermediary image transfer member cannot perfectly fit with the minute convexes and concaves of such rough paper. Accordingly, fine gaps are formed at such irregular minute spots. Because of these fine gaps, abnormal electrical discharge occurs thereat, which makes it practically impossible or at best difficult for an image to be transferred in a fine and faithful manner. For this reason, the quality of an image formed thereon is likely to be poor and lacking in fine fidelity when viewed as a whole.
In contrast, the second-mentioned type of an image formation apparatus of related art, which performs secondary image transfer by transferring an image from an intermediary image transfer member onto an image transfer fixation member and thereafter performs tertiary image transfer as well as image fixation by transferring the image from the image transfer fixation member onto an image transfer target matter and fixing the image thereon, makes it possible to effectively prevent the deterioration of image quality explained above even in a case where a sheet of printing paper that has a rough surface is used because image transfer and image fixation are performed at the same time and/or as a single step. Specifically, the reason why it is possible to effectively prevent the deterioration of image quality even for such rough paper is that toner becomes softened and/or melted through heating that is performed concurrently with image transfer so as to turn into agglomerate blocks having viscoelasticity, which makes it possible to achieve the successful transfer of such viscoelastic toner agglomerates for portions of an image corresponding to the minute convexes and concaves (i.e., fine gaps) of the image transfer target paper. For this reason, an image formation apparatus that is provided with an image transfer fixation apparatus has an advantage over an image formation apparatus that is not provided therewith in terms of image quality.
In addition, in the steps of the image transfer fixation method, there does not occur a state in which fine particles are placed on an image transfer target matter. For this reason, the image transfer fixation method has another advantage in that it is possible to provide a paper transport guide having a narrow width up to immediately before image transfer fixation. Thus, it is possible to ensure stable and reliable paper transport irrespective of paper types inclusive of thin paper and thick paper. That is, if the image transfer fixation method is used, it is possible to use a variety of paper for printing. Moreover, with the image transfer fixation method, it is possible to effectively reduce the rate of occurrence of paper jam errors and/or malfunctions.
In the image transfer fixation process explained above, the improvement of thermal efficiency is an important factor for excellent image transfer. In order to improve thermal efficiency, it is effective to raise interface temperature, that is, temperature between the surface of a sheet of recording paper and toner that adhere to each other. Conventionally, toner has been pre-heated well for the softening thereof. Then, the softened toner is fixed thereon through the application of pressure thereto. However, such a conventional method in which toner only is heated has a disadvantage in that it is practically impossible or at best difficult to achieve satisfactory thermal efficiency in a case where, for example, an image transfer fixation member has a large thickness such as 300 μm or so or in a case where a quad tandem full color image formation system that has a large perimeter is adopted. Especially, since a cooling step is required after an image transfer step, there is a lot of waste in terms of energy efficiency; that is, it is necessary to heat a target object and then cool the same target object.
In an effort to overcome such a disadvantage, there has been proposed a technique of heating the surface of a sheet of printing paper immediately before it becomes in contact with toner. Since not only the front side of a sheet of recording paper but also the reverse side thereof are heated in the above-mentioned proposed technique of the related art, the proposed technique cannot achieve high energy efficiency. Moreover, many outstanding problems remain unsolved, including but not limited to, the possible ignition of paper in a heating process, temperature unevenness, and scumming due to overheating.